In many different environments, signals may be monitored and analyzed to obtain information about the source of the signal. For example in one environment, electrodes of an electrocardiogram system may be positioned on a patient's body to sense and amplify electrocardiographic (ECG) signals originating from the patient's heart. The signal analyzer may then analyze the sensed and amplified ECG signals to obtain information about the condition of the patient's heart. In another environment, a vibration sensor may be positioned upon an operating automotive transmission to generate vibration signals that are indicative of the mechanical vibrations the transmission is experiencing during operation. A testing apparatus may then monitor and analyze the vibration signals generated by the operating transmission to determine whether the transmission has a mechanical defect.
One technique for analyzing the above signals has been to compare the frequency spectrum of the monitored signals to patterns or stencils that have been obtained from known signal sources. For example, several frequency spectra may be obtained from vibration signals generated by several properly operating transmissions. A technician may then analyze the obtained spectra and define a pattern or stencil which matches the obtained spectra. A testing apparatus then may monitor and compare the vibration signals generated by another transmission to the previously defined stencil in order to determine whether the monitored transmission is functioning correctly.
Similarly, several frequency spectra may be obtained from vibration signals generated by differential assemblies having a defective bearing. Again, a technician may analyze the obtained spectra and define a stencil which matches the obtained spectra. A testing apparatus then may monitor and compare the vibrations signals generated by another differential assembly to the previously defined stencil in order to determine whether the differential assembly has a defective bearing.
A disadvantage of the above signal analysis technique is that defining stencils is costly since a technician must analyze and manually define a stencil representative of signals having a known characteristic (e.g. proper functionality, defective bearing). As should be appreciated, analysis of the generated spectra by the technician is time consuming. Moreover, the time consuming analysis is amplified due to several stencils needing to be defined in order to monitor several types of components, and detect several types of conditions.
Another disadvantage of the above signal analysis technique is that the quality of the defined stencils is highly dependant upon the skill level of the technician defining the stencils. For example, if the technician defines a stencil too strictly, then a testing apparatus may fail to match a monitored signal to the defined signal even though the monitored signal was generated by a device having the condition represented by the defined stencil. Conversely, if the technician defines the stencil too broadly, then a testing apparatus may improperly match the monitored signal to the defined stencil even though the monitored signal was generated by a device not having the condition represented by the defined stencil.
What is needed, therefore, is a method and apparatus for automatically constructing stencils that are representative of signals having similar characteristics.